Intraoperative Aberrometry: Does It Improve IOL Power?

Intraoperative aberrometry measures the refraction of the eye in the operating room, after the cataract has been removed.

The surgeon uses the result to check or refine the choice of the IOL power and the axis of a toric lens.

It has the most to offer in eyes in which preoperative calculations are unreliable.

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How Intraoperative Aberrometry Works

A wavefront device is mounted on the operating microscope, and measures the refraction of the aphakic eye or the pseudophakic eye, in real time.

• The aphakic measurement gives the spherical equivalent and the astigmatism, which the software uses to recommend an IOL power
• In toric surgery, the device helps to identify the steep axis and to guide the alignment of the lens
• Some systems measure after lens implantation, to confirm the position and the refraction

The measurement can be affected by the chamber pressure, the eye position, and viscoelastic, so a standard routine is needed.

Intraoperative Aberrometry: Why It Might Help

Preoperative biometry and formulas are accurate in normal eyes, with most within half a diopter of the target (see IOL power calculation).

In unusual eyes, such as after laser vision correction, with very long or short axial length, or with irregular corneas, the errors are larger, and a direct measure of the eye after lens removal might reduce them.

What the Evidence Shows

• A large series reported that adding aphakic measurements improved the accuracy of the final refraction compared with preoperative calculations alone in several groups (see the references)
• Later studies compared the technique with modern formulas, such as Barrett and Kane, and found that the improvement was small or not significant in eyes of normal length (see the references)
• In post-LASIK eyes, results are promising but mixed, and the formulas for these eyes have also improved
• In toric surgery, the device may reduce residual astigmatism, but results differ between studies

The overall message is that it is helpful in selected cases, and not a replacement for good preoperative planning.

Intraoperative Aberrometry: Where It Is Most Useful

• Eyes after LASIK, PRK, or radial keratotomy, where keratometry is unreliable (see LASIK)
• Very short or very long eyes
• Eyes with irregular corneas, such as after keratoplasty
• Toric lenses, as a check of the alignment (see toric IOL misalignment)
• Surgeons seeking quality control of their results

Limitations of Intraoperative Aberrometry

• The cost of the device and the extra time in the operating room
• Variable results with pressure, lid position, and fixation
• Dependence on the platform, with different algorithms
• A need for the surgeon to know when to trust the intraoperative reading and when to follow the plan

Conflicts between the two methods require judgment, and the surgeon may use the average or the more reliable one.

Practical Tips

• Standardize the pressure, the lid speculum, and the eye position before each measurement
• Remove bubbles and viscoelastic, and keep the cornea wet
• Record both the preoperative and the intraoperative values, and compare them with the final refraction
• Audit the results, and adjust the lens constants if a bias is found

Auditing results for each surgeon and each device gives the most useful information (see refractive surprise after cataract surgery).

Counselling

Explain to the patient that the technology is an aid, and that it does not guarantee a perfect result.

Describe the benefit in terms of reducing the chance of a surprise.

Documenting and Learning From Cases

Create a simple log of each eye in which the device was used, including the preoperative recommendation, the intraoperative recommendation, the lens implanted, and the refraction at one month.

After a few dozen cases, a surgeon can see whether the device tends to push the lens power in a certain direction, and adjust the way that the information is used.

Cost and Workflow

The device adds time to the case, usually a minute or two, and requires staff training.

Some centers use it only in selected eyes, such as post-laser eyes and toric cases, to balance the cost and the benefit.

Looking Ahead

Software updates and artificial intelligence may improve the predictions.

Compare results with the newest preoperative formulas (see cataract surgery in high myopia).

Training the whole team in the setup of the device shortens the delay and improves the quality of the readings, so that the measurement adds to the case and does not interrupt it.

Discuss with your team which cases will use the device, set a clear rule for when to follow its advice, and review the outcomes together every few months to confirm that it adds value.

For the latest studies, see the PubMed results for intraoperative aberrometry.

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References

1. Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation prior to cataract surgery. Ophthalmology. 2014;121:56-60.
2. Raufi N, James C, Kuo A, Vann R. Intraoperative aberrometry vs modern preoperative formulas in predicting intraocular lens power. J Cataract Refract Surg. 2020;46:857-861.
3. Melles RB, Holladay JT, Chang WJ. Accuracy of intraocular lens calculation formulas. Ophthalmology. 2018;125:169-178.
4. American Academy of Ophthalmology. Basic and Clinical Science Course, Section 11: Lens and Cataract. AAO; current edition.